US ground forces are in northern Syria supporting the Syrian Democratic Forces
US forces returned fire after being repeatedly shot at near Manbij in northern Syria, where they are patrolling near areas held by Turkish-backed rebels, coalition spokesman Colonel Ryan Dillon said on Tuesday.
"Our forces did receive fire and return fire and then moved to a secure location," he said by phone.
The incident reflects the complexity of the battlefield in northern Syria, where the Russia-backed Syrian army, Kurdish forces aided by the US-led coalition and Syrian rebels supported by Washington's ally Turkey are all operating.
The coalition has told Turkey to tell the rebels it backs there that firing on US-led coalition forces "is not acceptable", Dillon said.
US ground forces are in northern Syria as part of the US-led coalition supporting the Syrian Democratic Forces (SDF), a local alliance of Kurdish and Arab militias battling Islamic State.
Last year, Turkey backed Syrian rebel groups in an offensive next to SDF-held areas aimed at both pushing Islamic State from the border and quelling the expansion of Kurdish influence.
The Turkish-backed rebels and the SDF have often exchanged small arms and artillery fire in other parts of northern Syria where US-led coalition forces are not patrolling.
"Our overt patrols that have been conducting patrols in that area to keep tensions down received fire multiple times over the course of the last two weeks," Dillon said.
"We let our counterparts in Turkey know this and we continue to conduct these patrols but are always prepared and ready to defend ourselves in that area."
US forces have been filmed since last year patrolling near Turkey-backed rebel areas while clearly displaying the US flag.
Russian military police have also carried out patrols in northern areas held by the Syrian army and by the Kurdish YPG militia, the main component of the SDF.
Coalition and US jets have carried out operations to prevent potential attacks on local forces they support.
A year ago, they scrambled to protect US special operations forces in northern Syria from attack by government jets during rare clashes between the Syrian army and the YPG.
In May, the US military carried out an air strike against militia supported by the Syrian government that posed a threat to US and US-backed fighters in southern Syria.